Three-phase Power Converter Research Articles

Modeling and Design of Islanding Detection Using Phase-Locked Loops in Three-Phase Grid-Interface Power Converters

Islanding detection is critical to safety and power quality as well as the control mode of grid-interface power converters. This paper addresses the islanding-detection methods on the basis of the grid synchronization instability mechanism. Although many modified phase-locked loop (PLL) methods have been proposed to achieve islanding detection, the PLL modeling and design are not clear in the existing literature and a cut-and-trail process is usually required during the design phase. This paper proposes a systematic PLL modeling and design approach to evaluate different frequency-based islanding-detection methods. Two different types of PLL-based islanding-detection solution are discussed, accounting for a majority of the existing methods. The first method is to modify the PLL to constantly move the stable equilibrium point. The second method is to modify the PLL small-signal characteristics to achieve a monotonic instability behavior under the islanded conditions. The design procedures of these methods are presented using the proposed PLL modeling approach. The impact of the modified PLLs to the converter's operation is also analyzed.

Voltage Source Converter Topology for High-Power Applications Serializing Three-Phase Converters and H-Bridges

This paper presents a three-phase voltage source converter (VSC) topology for high-power applications. The presented topology combines 12 power electronics building blocks (PEBBs), being the power rating of the proposed VSC topology that is 12 times the power rating of each PEBB. This power is equally shared between each PEBB without the need of any control action; therefore, the converter works as a single three-phase power converter. In order to demonstrate the good performance of the presented VSC topology, it has been simulated in the simulation tool Saber, and the results have been experimentally validated in a test bench of 80 kVA.

A New Hybrid Power Conditioner for Suppressing Harmonics and Neutral-Line Current in Three-Phase Four-Wire Distribution Power Systems

In this paper, a new hybrid power conditioner is proposed for suppressing harmonic currents and neutral-line current in three-phase four-wire distribution power systems. The proposed hybrid power conditioner is composed of a neutral-line current attenuator and a hybrid power filter. The hybrid power filter, configured by a three-phase power converter and a three-phase tuned power filter, is utilized to filter the nonzero-sequence harmonic currents in the three-phase four-wire distribution power system. The three-phase power converter is connected to the inductors of the three-phase tuned power filter in parallel, and its power rating can thus be reduced effectively. The tuned frequency of the three-phase tuned power filter is set at the fifth harmonic frequency. The neutral-line current suppressor is connected between the power capacitors of the three-phase tuned power filter and the neutral line to suppress the neutral-line current in the three-phase four-wire distribution power system. With the major fundamental voltage of the utility dropping across the power capacitors of the three-phase tuned power filter, the power rating of the neutral-line current suppressor can thus be reduced. Hence, the proposed hybrid power conditioner can effectively reduce the power rating of passive and active elements. A hardware prototype is developed to verify the performance of the proposed hybrid power conditioner. Experimental results show that the proposed hybrid power conditioner achieves expected performance.

Electric Loss Measurement Technique for Synchronous PM Brushless Machines

A novel technique to identify, by direct electric measurements, the total losses at full load in synchronous permanent-magnet brushless ac machines is here presented. The proposed procedure can anyway be extended to anisotropic machines. The procedure adopts a back-to-back electric and mechanic connection capable to use a single three-phase power converter to perform a full power test. The coupled motors are driven in speed as an equivalent electric machine at no load. The motor load can be regulated by the physical angular displacement in between the rotors of the two machines, and the converter will control the speed and equalize the current amplitude in the motors. In this condition, the motors exchange active power at the shaft in mechanical form and at the electric connections in electrical form. The active power supplied by the converter in steady state results in the total power dissipated by the two motors. A simple algorithm to identify the current-to-mechanical angle relationship at a given speed is proposed. The measurement technique is simulated and verified using an experimental test bench that adopts two low-power high-torque electric machines.

Fault detection and diagnosis in a set "inverter-switched reluctance motor" based on pattern recognition using Kalman filter prediction

In the case of one phase failure, the switched reluctance motor (SRM) will behave nearly the same, both in open circuit and in short circuit failure. This means, that the machine will understand the two faults in the same way which makes the SRM faults detection and diagnosis a more challenging task. This paper presents a diagnosis method based on pattern recognition analysis to detect and to classify automatically the electrical faults, short- and open-circuit under any level of load of the studied system: redundant three-phase power converter fed 6/4 SRM. The phases making a pattern recognition diagnosis of SRM, the training and the decision. The training phase consists in determining the pattern vector and the optimal kernels design (the separating classes) by Time-Frequency Representation (TFR). The training data is carried out using a set of fault scenarios, between healthy, single and combined faults, in terms of torque measurement at different load level, in order to deduce the fault severity. The second phase, consists in associating an unknown pattern with one of the defined classes, according to the k- nearest neighbors (knn) decision rule, associated with Kalman estimator to tracking of various operating modes and to predict the evolution of the call out of the knowledge database for a given operating mode in order to realize a preventive maintenance. The experimental results prove the efficiency of pattern recognition methods in condition monitoring of reluctance machine.

Grid-connected photovoltaic converters: Topology and grid interconnection

With the advances in high power converter technologies, photovoltaic (PV) power has been integrated into the utility system in greater pace in recent years. This paper aims to provide a broad overview of the various grid-connected PV system configurations and their power converter technologies for applications in single- and three-phase utility power systems. Grid-connected PV systems presented include module-integrated, string, and centralized configurations. Single- and three-phase power converters discussed include full-bridge (with an additional switch in the DC link and back-to-back IGBT on the AC terminals), and neutral point clamped converters. The synchronization techniques for grid-connected PV applications are discussed in this paper. An improved method to detect the grid frequency and voltage magnitude for single-phase system is introduced. More importantly, harmonic distortions resulting from the operation of grid-connected photovoltaic systems are addressed and analyzed. Methods for reducing harmonic currents using three types of passive filters, L, LC, and LCL, are presented. The LCL-filter design guidelines for a specific PV system are presented in detail. The effectiveness of these filters is demonstrated on 3 kW and 50 kW photovoltaic systems.

A Frequency Synchronization Method for a Self-Oscillating PWM Signal Generator

This brief proposes a frequency synchronization method for a full-digital self-oscillating pulsewidth modulation (PWM) signal generator. The self-oscillating PWM signal generator (PSG) generates a variable switching frequency, which results in poor drive performance for a three-phase power inverter or converter. The proposed frequency synchronization method utilizes an additional carrier signal, such as a triangular wave, to fix the switching frequency of a self-oscillating PSG. The switching frequency is synchronized by the triangular wave. As a test case, a switching frequency of 312.5 kHz is used for a performance evaluation of the proposed PSG with a sampling frequency of 12.5 MHz. A first-order noise-shaped output has been obtained. A high-precision PWM signal with low distortion and high resolution of the effective duty cycle has been achieved within the bandwidth. The proposed synchronized self-oscillating PSG is implemented in a three-phase brushless dc motor driver system to confirm the three-phase synchronization performance. Undesirable ripple current from asynchronous operation was not observed. The switching frequencies were synchronized among the three phases.

Analysis of Power Converter Losses in Vector Control System of a Self–Excited Induction Generator

Abstract This paper provides analysis of losses in the hysteresis-driven three-phase power converter with IGBTs and free-wheeling diodes. The converter under consideration is part of the self-excited induction generator (SEIG) vector control system. For the analysis, the SEIG vector control system is used in which the induction generator iron losses are taken into account. The power converter losses are determined by using a suitable loss estimation algorithm reported in literature. The chosen algorithm allows the power converter losses to be determined both by type (switching/conduction losses) and by converter component (IGBT/diode losses). The overall power converter losses are determined over wide ranges of rotor speed, dc-link voltage and load resistance, and subsequently used for offline correction of the overall control system’s losses (efficiency) obtained through control system simulations with an ideal power converter. The control system’s efficiency values obtained after the correction are compared with the measured values.

An Observer-Based Finite Control Set Model Predictive Control for Three-Phase Power Converters

Finite control set model predictive control (FCS-MPC) for three-phase power converters uses a discrete mathematical model of the power converter to predict the future current value for all possible switching states. The circuit parameters and measured input currents are necessary components. For this reason, parameter error and time delay of current signals may degrade the performance of the control system. In the previous studies of the FCS-MPC, few articles study these aspects in detail and almost no method is proposed to avoid these negative influences. This paper, first, investigates the negative impacts of inductance inaccuracy and AC-side current distortion due to the time delay caused by filter on FCS-MPC system. Then, it proposes an observer-based FCS-MPC approach with which the inductance error can be corrected, the current signal’s time delay caused by filter can be compensated, and therefore the performance of FCS-MPC will be improved. At last, as an example, it illustrates the effectiveness of the proposed approach with experimental testing results for a power converter.

A static and dynamic model of a space vector modulated matrix-reactance frequency converter

The determination of a converter's passive elements and loadability margin for various load and power grid conditions is of great importance to the proper operation of matrix-reactance frequency converters. The modulation strategy of power switches is very important to the voltage gain and input power factor control. The space vector modulation is the most commonly used algorithm for the control of three-phase power converters. In this paper the average-state space method and the two-frequency d–q transformation are proposed as aids in the process of fast verification of the matrix-reactance frequency converter operation under specific conditions. The experimental verification of the proposed model is also presented.

Switched Reluctance Motor Drive With External Rotor for Fan in Air Conditioner

This paper describes the developed three-phase 6/8 poles switched reluctance external rotor motor drive for a fan in air conditioner. The external rotor core structure and the internal stator core structure, the three-phase windings arrangement, the slotted claw, and the setting structure of the photoelectric transducers on the rotor position detector are illustrated. The electromagnetic field calculation results are given. The three-phase asymmetric bridge power converter was used in the drive system. The block diagram of the switched reluctance external rotor motor drive with closed-loop rotor speed control is given. The closed-loop rotor speed control is implemented using a fuzzy logic algorithm. The experimental tests of the developed prototype are made for driving the fan from 200 to 950 r/min. The comparison results of the two systems show that the input power and input phase current RMS value are lower in the developed three-phase 6/8 poles external rotor switched reluctance motor drive prototype with the fan than those in the induction motor variable-frequency variable-speed drive with the fan.

Acceleration Closed-Loop Control on a Switched Reluctance Linear Launcher

In this paper we describe a developed switched reluctance linear launcher system with diagrams and photographs, which consists of a three-phase 6/4 structure simple side-switched reluctance linear motor, a three-phase asymmetric bridge power converter, and a TMS320F28335 DSP digital controller. The acceleration closed-loop control of the mover is proposed and verified for the first time. The acceleration closed-loop control of the mover is implemented by a fuzzy control algorithm. The turn-on angle and the turn-off angle of the main switches in the power converter are fixed, and the triggering signals of the main switches are modulated by the pulse width modulation (PWM) signal. The deviation of the acceleration between the given acceleration and the feedback practical acceleration, and the variation from the deviation of the acceleration are the two input control parameters. The increment of the duty ratio of the PWM signal is the output control parameter. The duty ratio of the PWM signal is regulated based on the fuzzy control algorithm. Flow diagrams of the software, such as the main program, the encoder unit time interrupt subroutine, analog-to-digital converter interrupt subroutine, and the fuzzy control algorithm subroutine are given. The developed prototype is tested experimentally. It is shown that the velocity response of the mover is satisfactory.

Modeling of Switched Reluctance Linear Launcher

A nonlinear simulation model of switched reluctance linear launcher drive based on MATLAB platform is presented in this paper. It consists of a three-phase 6/4 structure simple side switched reluctance linear motor, a three-phase asymmetric bridge power converter, and a closed-loop velocity controller, which is integrated with the magnetization curves of the switched reluctance linear motor obtained by the two-dimension finite-element electromagnetic field calculation, the nonlinear electrical network model of the power converter, and the excitation/commutation/velocity control algorithms. Those include mover relative position calculation module, controller module, power converter module, phase winding modules, and velocity calculation module. The simulated phase current waveforms and velocity curves agree well with the tested phase current waveforms and velocity curves experimentally. It is shown that the proposed nonlinear simulation model of the three-phase 6/4 structure switched reluctance linear launcher system is valid.

Operation of a Three-Phase Power Converter Connected to a Distribution System

This paper presents the operation of a distributed generation (DG) system driven by a dc-dc step-up converter and a dc-ac voltage source inverter (VSI) interfaced with the power grid. To create a stable mode when different kinds of loads are connected locally or when working under contingency, the step-up converter must regulate the dc link voltage, allowing the VSI to stabilize its terminal voltage. The power flow between the grid and the DG is controlled by applying a power/voltage method that regulates the amplitude and the displacement of the grid voltage synthesized by the DG, while a phase-locked loop algorithm is used to synchronize the grid and DG. Additionally, a set of simulations are performed independent of the load type or its work regime (whether it is connected to the grid). The effectiveness of the proposed method is evaluated by experimental results.

Linear Quadratic Regulator for the Three-Phase Grid Connected Power Converter

This paper proposes a combined power quality-optimal control of the three-phase grid connected power converter. By using the technique of decoupling control, the mathematical model of the three-phase power converter is developed in the dq rotating reference frame and it is linearized around the operating point. The optimal control problem is with free-end point, infinite time horizon, and without constraints. The proposed optimal control is obtained as a solution of the Algebraic Riccati Equation. The numerical simulations based on the Matlab/Simulink software show the validity of the proposed solution.

Comparative Analysis of Three-Phase AC-DC Converters Using HIL-Simulation

This paper presents a comparative evaluation of various topologies for three-phase power converters using the hardware-in-the-loop (HIL) simulation technique. Various switch-mode AC-DC power converters are studied, and their performance with respect to total harmonic distortion (THD), efficiency, power factor and losses are analyzed. The HIL-simulation is implemented in an Altera Cyclone II DE2 Field Programmable Gate Array (FPGA) Board and in the Matlab/Simulink environment. A comparison of the simulation and HIL-simulation results is also provided.

Analysis, Design, and Experimental Verification of a Synchronous Reference Frame Voltage Control for Single-Phase Inverters

Control of three-phase power converters in the synchronous reference frame (SRF) is now a mature and well-developed research topic. However, for single-phase converters, it is not as well established as three-phase applications. This paper deals with the design of an SRF multiloop control strategy for single-phase inverter-based islanded distributed generation systems. The proposed controller uses an SRF proportional-integral controller to regulate the instantaneous output voltage, a capacitor current shaping loop in the stationary reference frame to provide active damping and improve both transient and steady-state performances, a voltage decoupling feedforward to improve the system robustness, and a multiresonant harmonic compensator to prevent low-order load current harmonics to distort the inverter output voltage. Since the voltage loop works in the SRF, it is not straightforward to fine tune the control parameters and evaluate the stability of the whole closed-loop system. To overcome this problem, the stationary reference frame equivalent of the voltage loop is derived. Then, a step-by-step systematic design procedure based on a frequency response approach is presented. Finally, the theoretical achievements are supported by experimental results.

Three-phase modular single stage full-bridge converter for switched mode power supplies

In this paper, the modular development of a three-phase single stage ac-dc power converter based on single-phase ac-dc isolated full-bridge converter for telecom power supply applications is presented. Three single-phase converter modules are series connected to form a three-phase converter system to achieve balanced three-phase currents. This paper analyses the operation of a modular converter in continuous conduction mode (CCM) of power factor correction. The performance of such a modular full-bridge converter system has been evaluated with simulation based on a MATLAB model and the results are also presented. The main objective of the proposed system is to reduce the number of stages and improve the power factor of the input ac mains current. The proposed scheme offers simple control strategy, electrically isolated output, single-stage power conversion, elimination of power transformer at the front end and inherent power factor correction (PFC) for medium rating power supplies.

Novel Microcontrollers With Direct Access to Flash Memory Benefit Implementation of Multi-Optimal Space Vector Modulation

This paper discusses a new architecture for the PWM generation in digital control hardware intended for control of three-phase power converters. The novelty of the proposed architecture is based on the use of emerging flash memory devices. An infinite number of state combinations and sequences is therefore available during a sampling interval. Three optimization criteria are herein simultaneously employed, dealing with optimal sharing of the zero sequence states, variation of the pulse frequency, and over-modulation through an optimal pattern. Performance is measured with the harmonic current factor and this is demonstrated to surpass the results of conventional implementation. The proposed architecture is versatile because it can be used at different sampling and fundamental frequencies, different operation modes, and without jeopardizing transient performance. While the current products allow implementation on external 64-MB flash memory, this architecture can be adopted in the future within the next-generation microcontrollers.

Series-voltage-action converter

This study presents a single- and three-phase power conversion topology based on series voltage action (SVA) to be employed in either dc-ac (inverter) or ac-dc (rectifier) power conversion systems. Each topology will be called as an SVA, that is, single- and three-phase SVA converter. The SVA converter is a configuration with specific advantages, such as (i) ac voltage higher than dc voltage with a single dc source, (ii) harmonic distortion improvements at ac converter side and (iii) reduced stress in each power switch. The complete analysis presented in this study includes the converter model, its operation, the modulation strategy, dc-link capacitor voltage and current. Also, a comparison with conventional converters has been carried out. Simulated and experimental results corroborate the theoretical study.